Make sure Documents timeline is selected, then type -myworkdomain.com into filter field. That should show all urls without myworkdomain.com.

Then on the right side there is an arrow pointing down, click it and choose Add to Autotag.


Another way to do similar thing:
Tag myworkdomain.com -> Work
Then tag your browser on applications timeline -> Non work.

Then in Autotag editor check "Match only first" and make sure that autotag Work is before Non work. If you do it this way it is easier to add sites to Work autotag. Because Work has higher priority you can easily add other sites to Work. For example you can just right click workrelatedsite.com and add it to Work autotag.

Hope I explained it well enough.